Automatic range tracking circuit



Aug. 27, 1957 J. R. ROGERS AUTOMATIC RANGE TRACKING CIRCUIT Filed Feb. l, 1946 as OQ mObDmPmo INVENTOR JOB ROBERT ROGERS ATTORNEY United States Patent Oiitiee 2,804,6l2 Patented Aug. 27,` 1957 AUTOMATIC RANGE TRACKING CIRCUIT Job R obert Rogers, Cambridge, Mass., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy l Application February 1, 1946, Serial No. 644,969

5 Claims. (Cl. 343-73) echo detection and automatic range tracking of a selected target. It contained provisions for automatically searching from Zero to maximum range of the echo detection system, and also a provision for-disconnecting the automatic search when a target was detected and a manual control for selecting targets if desired. The system is subject to certain limitations in automatically tracking a selected target echo, namely, tracking could be performed better on one edge of a target pulse and approaching targets could be tracked faster. VIn addition the means of automatically shifting from the auto-v matic search to the automatic tracking has been found not entirely satisfactory. The present application deals with improvements of the invention disclosed in the above application, and has as a primary object the provision of an improved electrical system of automatic searching and range tracking.

Another object is to provide an improved and more reliable system for automatically tracking a particular target echo.

A further object is to provide an improved system for automatically disconnecting the automatic search to enable automatic tracking of a particular target.

A still further object is to provide an improved automatic range tracking radar system having an automatic volume control provision in the receiver for controlling its gain so as to increase the rate of correction of the tracking circuit.

A still further object is to provide an improved automatic tracking radar system wherein an automatic search circuit is activated whenever the receiver fails to detect a target pulse at the setting of the automatic tracking circuit.

These and other objects will be apparent from the following specication when taken with the accompanying drawing which illustrates the features of the invention.

In order to present a clearer description of the invention it will first be described briefly with referencev to the figure. This brief description will also serve to review the operation of the earlier form of the invention given in the above application.

The systemiis used to search for targets by radio echo detection and to track any such target automatically when it is detected. A radar system is used in searching for and detecting targets. A range unit is used for automatic range tracking and a sawtooth generator in the range unit provides automatic searching,

The radar operates in the usual manner and in addition supplies a trigger pulse and echo known as a video signal to the range unit. The trigger pulse is supplied by the modulator to a precision delay multivibrator (hereinafter abbreviated MV) or other delay device 14. This MV 14 initiates and displaces in time two short pulses or narrow gates, known as an early gate and a late gate, which are developed inthe blocking oscillators (hereinafter abbreviated B. O.) 26 and 28. These pulses are displaced so that one starts as the other ends. These pulses are applied to the suppressor grids of the respective coincidence tubes 22 and 24. Video echo signals from the radar receiver are applied through a delay line 20 to the control grids of the coincidence tubes 22 and 24. The delay is provided to permit the early gate to precede the echo pulse even at zero range of the radar and to allow operation on the latter part of the delay sweep where linearity is better. lf there is coincidence between either or both gate pulses and the video pulse, one or both tubes will conduct in proportion to the relative time of overlap of the echo with respect to the gates. If there is no coincidence between the echo pulse and the gate pulses the coincidence tubes will not conduct and if coincidence occurs only between the echo pulse and one gate -pulse only the corresponding coincidence tube will conduct. The output from the coincidence tubes 22 and 24 is fed to the integrator circuit Sil. lf most of the echo pulse occurred during the early gate the integrator will reduce the voltage on capacitor 32 but if most of the echo pulse occurs during the later gate the voltage on capacitor 32 will increase. There will be a relative overlap of the echo pulse and the two gates for which the voltage on capacitor 32 will not change. This voltage is fed through the cathode follower 34 to the servo 36 which provides accurate range data, and also couples back to the MV 14 to correct the position of the narrow gates as necessary to continue tracking the echo pulse. The voltage on capacitor 32 will be proportional to target range. When no target is being tracked with the gates, there will not be an output from the coincidence tubes 22 and 24 and the detector tubes 54 and 56 will not be operating. This will allow the disconnector circuit composed of tube 62 and relay 44 to connect contact 46 to point 48.

Automatic range search is provided by sawtooth generator 42 the voltage output of which is coupled through contact 46 to the capacitor 32 at point 40. Thus, the variation of the potential on capacitor 3.2, will sweep the MV through the range of the radar until a target is found. When a target is located there will be an output from one or both of coincidence tubes 22 and 24. This will be detected by either or both detector tubes 54 and S6 which will operate the disconnector circuit to cause relay 44 to open the contact 46 and allow the automatic range tracking, described above, to operate.

An automatic volume control (hereinafter abbreviated AVC) composed of detector tube 64 and amplier 70 is provided to control the gain of receiver 18.

The operation of the improved range unit will now be discussed in detail with reference to the same iigure.

In the radar, the modulator 1t) supplies a periodic trigger to a transmitter 12 and a delay MV 14. This causes the transmitter 12 to tire and send out a high energy, high frequency pulse from antenna 16 which is returned from a target and detected by the receiver 18 after a time lapse equivalent to target range. The echo from receiver 18 is applied to the delay line 20 and then-ce to the control grids of the coincidence tubes 22 and 24. The delay MV 14 after receiving a trigger from modulator 10 introduces a variable delay and puts out a trigger to B. O.

26 which in turn puts out a positive square pulse (here-v inafter called a gate) with a trailing edge occurring at the time of the echo pulse as it comes from delay line 20. It also triggers B. O. 23 so that it puts out a square gate'like the gate fromB. O.` y26 which starts at approximately the time the first gate ends. ThusV the two square gates bracket the echo pulse. These gates are applied to the'suppressor grids of the respective coincidence tube 22- and 24. Y Y' If the echo pulse occurs between the two gates the-.extent of conduction and hence the outputs from tubesV 22 and 24 will be equal. If the echo pulse does not occur between the two gates 'out on either side then one or the other coincidence ytube will conduct more.` If the echo pulse and! Vgate do not occur together ineither coincidence Ytube there wil1not bel any output fromthe tube. The coincidence outputs are appliedV to the integrator circuit 36.' Integrator 30 will be unaffected when the applied pulses are equal.y However, if the echo pulse occurs early,tube 22 will.v conduct more than'24 and theinputs to theintegrator Stiwill be unequal. This then changes thevoltage `on capacitor32 accordingly, and this change is applied to cathode follower 34=and in turn'to the servo unit 36. `It will also be applied over lead 38 to the delay MV 14 tovary the delay` introduced byV MV 14 to reposition the gates so they will straddle theV echopulse from the radar. .The voltage from cathode follower 34 is1proportional to the range of the target: so thatthe servo may be used to drive a range indicator or other device.

. Thus it is seen that when a-target echo is detected it will be tracked automatically by the range unit, T o provide means for automaticallysearching for a target, the sawtooth generator and control circuit 42 are incorporated vinto the system. When no target is being. tracked relay A44 will have its contact arm 46 making contact; at terminal 4S; the latter being connected to the sawtooth here asalready explained will be fed back to MV 14. This sweep voltage will vary the delay of the MV 14, which will cause the gates to sweep over the range of thel detection systen1.

4When a ftarget is found which occurs at the time of the gates one or both of thejcoincidence tubes 22 or 24 will conduct depending on the positionk of the target echo'with respect-.tothe gates. The outputs from the two coincidence circuits 22 and 24 which are coupled through transimmers-23 and 25 are picked up at pointsS() and 52 and applied to the respective control grids of detector tubes S4'a-nd`56. Any output from coincidence tube 22 is detected by the detector tube. 54 and any output from coincidence tube .24 is detected. by the detector tube 56. The outputs from. the detector tubes 54 and 56 will appear at point S8 which is common to both cathodes. This resulting output which does not vary appreciably for wide changes of relative overlap between the echo pulseiand "circuit42. Circuit 42 will provide a sweep voltage which lwill be applied at tothecapacitor 32. The voltage the gates, isapplied through'V amplifier 60 to the grid of Y tube 62 in, the disconnector circuit. When tube 62 operates relay 44 breaks the contact 46. from pointV 48 to Vremove the search circuit 42 from the system. Thus, the automatic search system is automatically disconnected lwhena target is detected to permit automatic range tracking of the target within wider'limits because of the overlap between the echo pulse and both gates.

The tracking balance control. potentiometer 78 in the coincidence circuitsallows the relative bias on the two coincidencetubes 22 and 24 to be varied to control the conduction 4ratio of one coincidence tube withv respect to Y the other.V In this way slight differences in the tubes can be adjusted for. In' addition this adjustment can be varied. effectively to change the position whichthe Vdouble gates assume with'resp'ect to the echopulse envelope. This. allows `favoring of4k approaching or receding .targets by varying the. tracking balance control 78. v

To.provide for further control ofi the range unit an at'ltontaticvolurnel control circuit is used Thisis. energized from. tap 66 the midpoint of .resistor 72 which is connected between the output points 74 and 76 of the coincidence vtransformer secondary circuits. The voltage from tap 66 is applied to the grid of the AVC tube 64. The output is taken at point 68 on the cathode and fed through an appropriate amplifier and coupling cathode follower 70 to the radar receiver'1`8. When the echo from the receiver occurs at thek midpoint of the gates. from the blocking oscillators 26 and 28, the outputsY from both coincidence circuits at 74.` and 76 willcontribute to the voltage atrpoint 66 fromwhich the` AVCl detector 64 .Y

is energized. If the echo gets off Yto eitherside ofthe center-of the gates one coincidence tube will4 put out a larger signal than the other.` This will cause a rise in voltage at terminal 66 and the gridof`tube'64 which will l increase `the output of the AVC detector 64. The vAVC detector 64 has a narrower characteristic than the detector tubes 54 andV 56 and' causes the AVC todrop otfrst and give maximum/gain before the detectorcircuit allows` ent arrangement the VAVC is `particularly sensitive to the phase relation of the target signal and tracking gates and is unsymmetrical inv this respect. That is, it can be made to track readily onv either approaching or-receding targets.' In the detector disclosed hereinabove the gatesV may be phased in range relative to they signal with slight change in the detector-,output over a wide range. The detector output is chiey dependent on the coincidence tube grid with the greatest positive swing.V Thus since the outputs of both coincidence tubes 22 and 24 are detected, the tracking balancecontrol 78 may be adjusted so that the gates-track on the leading. orf on the trailing edge of the video pulse. If the gates track on the trailingedge of the l video the early gate will assume the' burden and will chiefly control the output of thedetector. If the gates track on theleading edge of the video the late gate will chieily control the output of the detector. 'Ihusit may be seen that the loutput of the detector is not too critically related to the relative position or overlapof the gate with respect to the video pulse and the gates can be phased relative to the signal without altering the threshold value at which the disconnector circuit operates. Similarly,v when the speed of tracking varies, it is obvious that the position-of the gates relative to the video will vary, and withthefnew arrangement, this relative position does not control the threshold of the disconnector circuit.

The improved systemrthusprovides more reliable automatic trackin-g'of approaching or receding targets as predetermined; and` more accurate control of the automaticrswitching between automatic search and automatic tracking.

. It-is'Y believed that the construction' and voperation. as

well as the advantages of the improved range unit will be'apparent'from the foregoing detailed descrip-tion thereof. Itwill also -be apparent that while I have shown and described my invention in a preferred form changes may be'mad'e in the circuit disclosed without departingY from-the spirit ofthe invention as sought toV be defined' v in the followingclairns.

Whatis claimed is:

1. In combination with aradio pulse object locating system having'. a transmitter for periodicallyV radiating radio frequency search` pulses and a'receiver for subsequently detecting these pulses afterj reflection from remote targets an automatic range tracking circuit.' rsaid circuit including meansforicomparing the time of o c- 'Y currence cfa; selectedtarget pulse detected by said receiverwith" rst and second consecutive gate 'pulses geni' erated'a; controllable time aftrtffthe; radiation ofpsaid search pulsesgan'd'lfor. producing rstand second signals having amplitudes proportional to the amount of coincidence between said target pulse and each of said gate pulses, an automatic gain control circuit included in said receiver, means responsive to the production of unequal amplitude first and second signals for controlling said automatic gain control circuit to thereby increase the gain of said receiver whereby the following selected target pulse compared with said consecutive -gate pulses has increased amplitude and whereby as a consequence the amplitude inequality of said first and second signals is magnified, means for deriving an error signal proportional to the difference in amplitudes of said first and second signals and means controlled by said error signal for changing the time of occurrence of said consecutive gate pulses with respect to the time at which said search pulses are radiated to equalize the amplitudes of said rst and second signals and thereby minimize said error signal, said last mentioned means providing an indication of the range of the target corresponding to said selected target pulse.

2. In a system as defined in claim 1 wherein said means for increasing the lgain of said receiver in response to the production of unequal amplitude first and second signals comprises an electron tube having its plate connected to a reference potential and its cathode coupled to a negative source of potential through a cathode resistor, means coupled to the grid of said tube for increasing its conductivity whenever unequal amplitude first and second signals are produced, means for connecting the cathode of said tube to the input of the automatic gain control circuit of said receiver, said electron tube performing as a relatively short time constant detector by virtue of t-he distributed capacitance of said cathode resistor.

3. In a system as defined in claim 2, means responsive to the nonproduction of bot-h said first and second signals for substituting for said error signal a sawtooth voltage wave whereby the time of occurrence of said consecutive gate pulses is cyclically varied, said last mentioned voltage source being rendered ineffective whenever said selected target pulse coincides with a portion of either said first or second gate pulses.

4. In a system as defined in claim 2 wherein said means for cyclically varying the time of occurrence of said consecutive gate pulses comprises a double detector including first and second electron tubes, means for connecting the plates of said tubes to a reference potential and the cathodes of said tubes through a parallel resistance-capacitance network to a negative source of potential, means for applying blocking biases to the control grids of said tubes and means for selectively reducing said blocking biases in response to the production of either a first or second signal whereby an output voltage is produced across said network, a sawtooth voltage source adapted to be substituted for said error signal for changing the time of occurrence of said consecutive gate pulses, said last-mentioned voltage source being maintained ineffective by the output voltage from said electron tubes.

5. In combination with a radio pulse object locating system having a transmitter for periodically radiating radio frequency search pulses and a receiver for subsequently detecting these pulses after reflection from remote targets, an automatic range tracking: and searching circuit comprising means for comparing the time of occurrence of a selected target pulse detected by said receiver with first and second consecutive rectangular gate pulses generated a controllable time after the radiation of each search pulse and for producing first and second signals having amplitudes proportional to the amount of time coincidence between said target pulse and said first and second consecutive gate pulses, respectively, an automatic gain control circuit associated with said receiver, means for deriving from said rst and `second signals a control signal whose amplitude is proportional to the average value of said first and second signals, a first detector, said detector comprising a cathode follower amplifying stage, means for coupling said control signal to the control grid of said cathode follower amplifier stage, means for feeding the voltage developed across the cathode resistor of said amplifying stage to the automatic gain control circuit to increase its gain in response to decreases in the average value of said first and second signals whereby the following selected target pulse detected by said receiver has its amplitude increased, means for deriving from said first and second signals an error signal having an amplitude proportional to the difference in amplitudes of said first and second signals, said error signal controlling the time of occurrence of said consecutive rectangular gate pulse with respect to the time at which each search pulse is radiated so as to equalize the amplitudes of said first and second signals, a second detector, said second detector comprising first and second triodes having their plates and cathodes interconnected so as to be in parallel and sharing a common cathode resistor, means for coupling said first and second signals to the control grids of said first and second triodes, respectively, and means responsive to a predetermined decrease in the Voltage developed across said common cathode resistor brought about by the absence from said control grids of both said first and second signals for cyclically varying the time of occurrence of said consecutive rectangular gate pulses until a first or second signal appears on the control grid of either said first or said second triode.

References Cited in the file of this patent UNITED STATES PATENTS 2,409,448 Rost Oct. l5, 1946 2,410,424 Brown Nov. 5, 1946 2,412,612 Godet Dec. 17, 1946 2,416,591 Muntz Feb. 25, 1947 2,433,681 Blumlein Dec. 30, 1947 2,517,540 Busignies Aug. 8, 1950 2,628,349 Nightenhelser Feb. 10, 1953 

